Epic AOS Problems

Was hoping the community could help me troubleshoot an issue/ease my concerns: Issue --> My new 996 race car has a penchant for blowing the AOS; the first time after 30 laps the second after only 4. I know this is a common occurrence on these cars, but to fail so quickly back to back makes me believe the primary cause may be tangentially related to the AOS and not directly (perhaps a plugged exhaust line creating a vacuum?). Pertinent Facts: Stock engine (2 hours on rebuild) I keep the oil level low Both times it blew on hard, sweeping right hand corners (actually blew at virtually the same spot on track both times) Oil pressure good; air/oil temp good Has anyone experienced anything this prolific before? Any ideas on causes outside of AOS? And yes, the motorsports AOS is going into the car this time around.

What do you mean "blowing the AOS"? You mean the AOS has actually failed creating white smoke or it just blew smoke out the exhaust when cornering? Excessive crankcase pressure, possibly piston ring blowby? It really is just a crankcase pollution control device that separates air/oil vapors without bleeding them to the atmosphere. If the crankcase pressure gets to high then I could see where the AOS might fail. Maybe you need a oil pan with the separator plates that prevent the oil sloshing around during hard turns or on banking. I know there are some racers out there with some experience with this symptom, and how to prevent it. Sounds like you are headed in the right direction with the Motorsports AOS and need to think about adding an oil pan upgrade. My two cents.....

Isn't low oil levels plus long right-hand sweepers pretty much the formula for oil starvation for the M96? From LN Engineering's site, ..."the scavenge pumps and associated oil return passages (and de-foamers) cannot return and process the oil fast enough AND that under high G-forces, oil is trapped in the cylinder heads and is not scavenged back to the sump." http://lnengineering.com/resources/2...m96m97-engine/

Everything I've read over the years indicates that a deep-sump pan with better baffles is essential for M96-powered track cars, maybe with an Accusump thrown in for good measure.

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Both were catastrophic AOS failures....spy hunter smoke screen style. Crankcase pressure is an interesting thought, but wouldn't I see a spike in engine temp (forgive the naivet�)? Data shows oil pressure is relatively constant throughout, so not sure that could be the culprit.

Giving it more thought - I think on the sweeping right hand turns the oil is g-forced to the left side of the engine where the AOS crankcase port is located, so you are actually getting oil forced up the port into the AOS and the pressure blows it. It really is designed to handle crankcase vapor, not a full load of oil. 5CHN3LL is correct on both accounts. You need a deep sump oil pan with the baffles that keep the oil under the pickup tubes for racing and cornering. You are going to blow your engine from oil starvation from the high cornering forces and the first symptom is showing, blowing your AOS and subsequently getting oil in your intake manifolds creating huge amounts of smoke. Also, after installing a deep sump oil pan with baffles, I would not recommend running the engine oil level low. Again, a recipe for disaster if you ask me. I don't think that excessive crankcase pressure would equate to higher engine temp, but I would do some research on that.

Swamping the AOS by side loading the sump on sweepers.

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Makes sense. Looks like I'll be adding a deep sump and baffle kit to the parts order. Spending money to save money. Racing is a stupid hobby.

Heh. While true, the cost of an oil pan is somewhat less than another M96 rebuild. I had to take a break from autocrossing because I can't afford the damn tires right now...

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Those are good mods but unlikely to make a difference to the AOS. You should consider a Motorsport AOS.

yeah if your racing spend the $ on the motorsport AOS

If you're going to go racing you're going to have to fork over $ for modifications. Albeit the Porsche has a great heritage of racing, I've never heard of someone taking a stock car, racing it, and then complaining that it doesn't work right. What about tires and suspension mods? Would you take a stock Honda or Toyota out racing without any modifications? Get the Motorsport AOS and do the deep sump oil pan w/baffles. But also keep in mind that racing a car puts massive loads on it and the weak points will always so up on the track. That's why race teams spend the big $ prepping a car....

Wow These run about $600 (WOW) from Porsche.

Here's a comment from the Pelican thread about the motorsport AOS: "It is worth it if you are tracking your car and running R compounds. the stock one will let oil into the intake at high g's that totally cover the track with smoke and you could hydro lock your engine if enough of it gets there. Since I installed the motorsport AOS this problem never reoccurred. It's easy install on 03& 04 but a little mods is needed for earlier cars"

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Agreed. Like I said in the original post, the motorsports AOS is the first thing going in, I just wanted to be sure another problem didn't exist that could blow an $800 part in 10 minutes The car is a full build race car, basically how motorsports would build the 996 Cup if they produced it today. Only somewhat original 996 part is the engine, which I purposely used hoping to get a 125 hour car. I could have purchased a 6cup for less than what I'm into (which would also be less advanced), but I didn't want to spend $40k every two seasons to rebuild the drivetrain.

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Can't be sure something's not amiss. I'm a bit worried two stock AOS's failed so soon. Did you cut them apart and determine what failed? I'd want to be sure the AOS was installed correctly and hooked up correctly. Also, that if any restrictor or anti-backfire valve was required it was installed properly. My thinking is possibly the AOS could have been killed by something wrong with the installation.

Oops. Can't read. Edited.

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I've about gone through my second stock AOS in my 996 Carrera 4S and am about to have my shop put in the Motorsports AOS. I regret not doing it last time, since I paid ~7 hrs of labor and will now pay for that again. I track my car a lot -- maybe 12 days/year -- on Hoosier R6s. On track days I regularly have a lot of smoke at startup; then it's fine. Sometimes in the quick right-left transition of Turns 3-4 at Thunderhill I'll blow out loads of smoke for a few seconds ... I've concluded this is more likely to happen with too much oil in the pan (e.g., over 1/3 or 1/2). Is Porsche's AOS just poorly engineered in the first place?

The AOS was engineered perfectly for its intended use- sitting in the garage under a cover. Just an FYI, I talked to Jake Raby about getting one on my X51 engine, and apparently they won't fit in the engine bay with the x51 intake or something like that.

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Exactly what I told the OP at the track. Our cars are very similar and I've never smoked a stock AOS in 4 years of racing on slicks (x51 pan, no deep sump or accusump). I did replace one when I rebuilt the motor but its weird that his keep failing.....